>>Ukraine did not have the strongest military ready for NATO membership

It was more a matter of having borders under dispute. Those two provinces did break away from Ukraine after the Maidan Revolution. That alone would have kept them out of both NATO and the EU. I'm of mixed opinion as to whether that breaking away was spontaneous or had some Russian 'help'. But at the time, it looked (to me - very much not an expert) a kind of a civil war.

To the extent that the population in those areas, and Crimea still want to be part of the RF, the RF seems to have a legit case here - but not elsewhere in Ukraine. I'd also point out that there are dragnets of military recruiters roaming the RF controlled areas, conscripting anyone male and under 45-50 as cannon fodder, so those pro-RF sentiments, if they were there, might be shifting away.

Just a thought.